1. Field of the Invention
The present invention relates to a photographic coupler, and more particularly to a novel yellow color forming coupler which is suitable for use in the formation of color photographic images.
2. Description of the Prior Art
In the formation of color photographic images by a subtractive color reproduction process, an aromatic primary amine compound, especially a N,N-disubstituted para-phenylenediamine compound, is used as a developing agent, to reduce the silver halide grains in an exposed photographic emulsion layer, and the concurrently produced oxidation product of the developing agent is coupled with the color forming coupler to form a cyan, magenta or yellow image dye.
Couplers for use in the color developing process are compounds which have a phenolic hydroxy group, an anilinic amino group or an active methylene group, and, by coupling with the oxidation product of the aromatic primary amine developing agent form dyes which absorb light in the visible wave length range.
The yellow dye images exhibit a specific absorption to blue light in the wave length region ranging from about 400 to 500 millimicrons. Previously known yellow color forming couplers include .beta.-ketoacetoacetic esters, .beta.-diketones, N,N-malonic diamides and .alpha.-acylacetamides, and the like.
Of these compounds, pivaloyl acetanilide type compounds as described in U.S. Pat. No. 3,265,506 are widely used, as yellow color forming couplers, in the field of color photography. Although this series of couplers has many preferred properties, they also have a number of disadvantages and are by no means completely satisfactory. For instance, these couplers generally have poor coupling reactivity, the dyes which are formed from these couplers upon color development with certain useful color developing agents have poor fastness to light, and the leuco dyes formed upon color development are highly stable and further oxidation of the leuco dyes to form the dye by treatment in a strong oxidizing bath is necessary.
Also .alpha.-phenoxy-iso-butyryl acetanilide type couplers as described in German Patent Application OLS No. 1,956,281 and U.S. Pat. No. 3,770,446 are not satisfactory. These couplers have the disadvantages in that the dyes formed from these couplers have an absorption maximum in a relatively short wave length range and have a broad absorption into a longer wave length range, resulting in poor color reproduction, in that the preparation of the corresponding .beta.-ketoesters which are the starting materials of the couplers includes difficult procedures and the yields are poor, and the like.